Establishing a second population of the flax snail in New Zealand

Summary

The flax snail (Placostylus ambagiosus paraspiritus), Vulnerable and confined to a single erosion-prone colony at the base of New Zealand's Cape Maria van Diemen peninsula, was the subject of an experimental 1990 wild-to-wild translocation testing whether new colonies could be established as insurance against the loss of the sole surviving population, drawing from a source colony large enough (hundreds to thousands of snails) to sustain limited removal. In May 1990, 25 adults and six sub-adults were released at a moister northern site and 25 adults and seven sub-adults at a drier southern site 100 meters apart, each individually numbered and measured, with rodent bait stations established at both sites nine months beforehand and reactivated at the parent colony. Three months post-release, ten adults were confirmed alive at the northern site and nine at the southern site, some having moved up to 6.5 meters; juveniles were first recorded 18 months later, growing faster than in the parent colony, at roughly 17mm of shell height per year. A 1998 experiment intensified rodent control alternately at each site, but northern-site poisoning was extended beyond the planned two years once large juveniles and sub-adults began appearing there, while the southern site's drier, more open habitat and less intensive predator control ultimately led that population to fail. Major difficulties included the source colony's vulnerability to coastal erosion and balancing predator-control intensity against practical constraints. The project rates itself Partially Successful, with the northern translocation flourishing under adequate predator control while the southern translocation failed from insufficient protection in less suitable habitat.